U.S. patent application number 10/244538 was filed with the patent office on 2003-03-27 for method and apparatus for timing rotors in a rotary lobe pump.
Invention is credited to Hagen, Curt, Norman, Drew Van.
Application Number | 20030059330 10/244538 |
Document ID | / |
Family ID | 26936610 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030059330 |
Kind Code |
A1 |
Norman, Drew Van ; et
al. |
March 27, 2003 |
Method and apparatus for timing rotors in a rotary lobe pump
Abstract
A rotary lobe pump includes two geared-together,
counter-rotating shafts, to which are affixed rotors with
interdigital lobes. Adjustment of the angular relationship of the
rotors uses a clamping device within each rotor. The clamping
device consists of a tapered, slotted bushing that is forced
between a mating taper on the rotor and a locking device on the
shaft by means of a flanged fastener mated to each pump shaft's
threads.
Inventors: |
Norman, Drew Van;
(Whitewater, WI) ; Hagen, Curt; (Delvan,
WI) |
Correspondence
Address: |
BAKER + HOSTETLER LLP
WASHINGTON SQUARE, SUITE 1100
1050 CONNECTICUT AVE. N.W.
WASHINGTON
DC
20036-5304
US
|
Family ID: |
26936610 |
Appl. No.: |
10/244538 |
Filed: |
September 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60324525 |
Sep 26, 2001 |
|
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|
Current U.S.
Class: |
418/206.1 |
Current CPC
Class: |
Y10T 403/7058 20150115;
F04C 2/126 20130101; F04C 2230/60 20130101; F04C 15/0076 20130101;
F05C 2201/046 20130101; Y10T 403/7056 20150115 |
Class at
Publication: |
418/206.1 |
International
Class: |
F04C 002/18; F04C
015/00 |
Claims
What is claimed is:
1. A pump for pumping material, comprising: a first shaft; a first
tapered bushing, sized to fit said first shaft; a first rotor,
fitting said first shaft, with an internal tapered region fitted to
said first tapered bushing; and a first threaded fastening device
that urges said first rotor and said first shaft into frictional
contact with said first bushing.
2. The pump of claim 1, further comprising: a second shaft; and a
second rotor fitting said second shaft.
3. The pump of claim 2, further comprising: a second tapered
bushing sized to fit said second shaft, wherein said second rotor
has an internal tapered region fitted to said second tapered
bushing; and a second threaded fastening device that urges said
second rotor and said second shaft into frictional contact with
said second bushing.
4. The pump of claim 2, further comprising: a first gear, sized to
fit to said first shaft.
5. The pump of claim 4, further comprising: a second gear, sized to
fit said second shaft, configured to mesh with said first gear to
cause said first and second shafts to rotate in opposite directions
at the same rate.
6. The pump of claim 1, further comprising: a threaded section on
said first shaft that mates with said first threaded fasting
device, allowing said first threaded fastening device to urge said
first tapered bushing into frictional contact with said first rotor
and said first shaft.
7. The pump of claim 6, further comprising: a first shoulder on
said first shaft, positioned to provide a stop face against which
said first rotor rests when said first threaded fastening device
urges said first tapered bushing between said first rotor and said
first shaft.
8. The pump of claim 1, further comprising: a first flat on said
first shaft, positioned to engage said first tapered bushing and
prevent rotation of said first tapered bushing relative to said
first shaft.
9. The pump of claim 1, further comprising: a first plurality of
flats on said first shaft, positioned to engage said first tapered
bushing and prevent rotation of said first tapered bushing relative
to said first shaft.
10. The pump of claim 1, further comprising: a first keyway and key
assembly on said first shaft, positioned to engage said first
tapered bushing and prevent rotation of said first tapered bushing
relative to said first shaft.
11. The pump of claim 2, further comprising: a threaded section on
said second shaft that mates with said second threaded fasting
device, allowing said second threaded fastening device to urge said
second tapered bushing into frictional contact with said second
rotor and said second shaft.
12. The pump of claim 11, further comprising: a second shoulder on
said second shaft, positioned to provide a stop face against which
said second rotor rests when said second threaded fastening device
urges said second tapered bushing between said second rotor and
said second shaft.
13. The pump of claim 11, further comprising: a second flat on said
second shaft, positioned to engage said second tapered bushing and
prevent rotation of said second tapered bushing relative to said
second shaft.
14. The pump of claim 11, further comprising: a second plurality of
flats on said second shaft, positioned to engage said second
tapered bushing and prevent rotation of said second tapered bushing
relative to said second shaft.
15. The pump of claim 11, further comprising: a second keyway and
key assembly on said second shaft, positioned to engage said second
tapered bushing and prevent rotation of said second tapered bushing
relative to said second shaft.
16. The pump of claim 1, wherein: said second rotor is keyed to
said second shaft, to rotate therewith.
17. The first shaft of claim 1, further comprising: a rotary power
source; and a drive connection, that connects said first shaft to
said rotary power source.
18. The pump of claim 3, further comprising: a housing for said
pump, enclosing said first and second rotors, said first and second
shafts, and said first and second bushings; a bearing system to
support said first and second shafts for rotation within said
housing; and a shaft sealing system that seals the pumped material
from the bearing system;
19. The pump of claim 3, further comprising: a chamber within which
said rotors rotate.
20. An apparatus for setting timing of a rotor configured to mesh
with an identical rotor in overlapping rotational paths in a rotary
lobe pump, comprising: a tapered bushing; a shaft configured to
accept the rotor; and a threaded fasting device securing said
bushing, the rotor, and said shaft to rotate together.
21. An apparatus for setting timing of a rotor configured to mesh
with an identical rotor in overlapping rotational paths in a rotary
lobe pump, comprising: a tapered bushing; a shaft configured to
accept the rotor; and means for securing said bushing, the rotor,
and said shaft to rotate together.
22. A method for providing adjustable timing of lobe pump rotors,
comprising the steps of: equipping each rotor with a tapered inner
mating surface; equipping each rotor with a rear stopping surface;
driving each rotor with a drive shaft having a shoulder that mates
to a rear stopping surface of the rotor; locating a tapered bushing
between at least one of the shafts and its respective rotor; and
applying compression normal to the inner mating surface of the
rotor to secure the bushing, rotor, and shaft together.
23. The method of claim 22, wherein the step of applying
compression includes tightening a nut threaded onto the shaft.
Description
PRIORITY OF INVENTION
[0001] The application claims priority to U.S. Provisional Patent
Application Serial No. 60/324,525 filed Sep. 26, 2001, the
disclosure of which is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to rotary lobe
pumps. More particularly, the present invention relates to rotary
lobe pump timing adjustment.
BACKGROUND OF THE INVENTION
[0003] Rotary lobe pumps are used in industry for
positive-displacement pumping of foodstuffs, pharmaceuticals, and
other materials requiring avoidance of cross-contamination, freedom
from chemical interaction with a wide range of substances, and good
mechanical strength. Dimensional tolerances in all parts of the
pumps, especially in the vicinity of the working lobes, are
extremely close. Tight, uniform tolerances between the lobes of the
two rotors and between the rotor tips and the walls of the pumping
chamber are desirable because insufficient clearance results in
binding and wear, while excessive clearance reduces pumping
efficiency.
[0004] The requirements for strength, low contamination, and
inertness lead to the use of 316 corrosion resistant ("stainless")
steel (CRS), special alloys, or the like for parts exposed to the
materials being pumped. Parts fabricated of such alloys can be
sterilized and satisfy structural and producibility needs.
[0005] The two rotors comprising the materials-handling part of
rotary lobe pumps are geared together with tight-tolerance spur
gears, helical gears, or another low-lash, positive mesh design.
Such pumps use rather long drive shafts between the
materials-handling end and the drive end of the pump, ensuring
dimensional stability--the long intermediate region housing the
bearings holds the shafts rigidly parallel. Typical designs also
provide a degree of thermal isolation, as well as physical
separation between the materials-handling end and the drive
end.
[0006] In food and drug applications, Federal and state regulations
call for disassembly for cleanliness inspections and operational
tests on the order of once per day to once per month for pumps in
continuous use. Standard procedures in the user industries call for
testing in place (removal of front cover, visual exam, shim test,
and possible swab for culture) preceded and followed by a cleaning
flush. If the shim test fails, the typical previous design of pump
must be removed from the system, taken to a shop, and
overhauled.
[0007] For previous designs, the rotors are keyed or otherwise
rigidly attached to their shafts, while friction clamping on the
gears at the drive end of the shafts fixes the rotational
relationship, termed here the timing, between the shafts. For such
designs, timing adjustment requires disassembly of piping and
demounting of the pump, then removing access covers on the drive
end for adjustment and on the materials-handling end for
measurement. The adjustable gear clamp must be loosened, shims set
in place between the rotor lobes, the assembly tightened again, and
the workmanship checked by moving the shims to critical locations
and rotating the shafts. Finally, the entire assembly must be
lubricated, sterilized, and remounted to the machine from which it
was removed.
[0008] Materials being pumped can contain foreign or oversized
particles that migrate to the points of least clearance. Such
obstructions can cause transient torque spikes to be applied
between the two rotors or between the rotors and their driving
mechanisms. This in turn can exceed the friction limits of the
clamping devices, resulting in alignment shift. Unless the shift
causes noticeable anomalies--noise, slowing of drive motors, and
the like--such errors ordinarily remain in the system until the
next periodic servicing event.
[0009] Accordingly it is desirable to provide a rotary lobe pump
that simplifies maintenance by leaving the drive end of the pump
sealed during routine timing adjustment.
SUMMARY OF THE INVENTION
[0010] It is therefore a feature and advantage of the present
invention to provide the capability to relocate the adjustment
provision of rotary lobe pump timing to the materials-handling end
of the pump.
[0011] It is another feature and advantage of the present invention
to provide continuously adjustable timing through use of slotted,
tapered bushings.
[0012] It is another feature and advantage of the present invention
to permit routine maintenance with unimpaired precision while the
pump remains in place on the machine of which it forms a part.
[0013] It is another feature and advantage of the present invention
to have the ability to leave gear mesh at the drive end of the pump
intact during pump lobe timing adjustment.
[0014] The above and other features and advantages are achieved by
a novel method of fixing lobe pump rotors, as herein disclosed. In
accordance with one embodiment of the present invention, a pump for
pumping material comprises a first shaft, a first tapered bushing,
sized to fit the first shaft, a first rotor, fitting the first
shaft, with an internal tapered region fitted to the first tapered
bushing, and a first threaded fastening device that urges the first
rotor and the first shaft into frictional contact with the first
bushing.
[0015] In another aspect, the invention provides apparatus for
setting timing of rotors in a rotary lobe pump, comprising a
tapered bushing; a rotor configured to mesh with an identical rotor
in overlapping rotational paths; a shaft configured to accept the
rotor; and means, such as a threaded fastening device, for securing
the bushing, rotor, and shaft together.
[0016] In another aspect, the invention provides a method for
providing adjustable timing of lobe pump rotors, comprising the
steps of equipping each rotor with a tapered inner mating surface;
equipping each rotor with a flat rear mating surface; driving each
rotor with a drive shaft having a shoulder that mates to a flat
rear mating surface of the rotor; locating a tapered bushing
between at least one of the shafts and its respective rotor; and
applying compression normal to the inner mating surface of the
rotor to secure the bushing, rotor, and shaft together.
[0017] There have thus been outlined, rather broadly, the more
important features of the invention in order that the detailed
description thereof that follows may be better understood, and in
order that the present contribution to the art may be better
appreciated. There are, of course, additional features of the
invention that will be described below and which will form the
subject matter of the claims appended hereto.
[0018] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and to the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein, as well as the
abstract, are for the purpose of description and should not be
regarded as limiting.
[0019] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 provides a perspective view illustrating the overall
appearance of a preferred embodiment of the present invention.
[0021] FIG. 2 provides a partially disassembled view illustrating
the relationship between the rotors, housing, and ports of a
preferred embodiment of the present invention.
[0022] FIG. 3 provides an exploded view of a nut, a bushing, a
rotor, and a shaft to illustrate the way in which the elements at
the materials-handling end of a preferred embodiment of the present
invention go together.
[0023] FIG. 4 provides a section view along the axis of the
parallel drive shafts showing the relationship between the
components of a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0024] The invention provides a novel rotor attachment technique
that can retain full mechanical strength in all parts of the pump,
provide unimpaired ability to adjust spacing between the rotors,
and leave the drive end of the pump untouched during timing
adjustment. Embodiments of the invention accomplish this by keying
or otherwise rigidly attaching the gears to the drive ends of the
two shafts and using tapered-bushing clamping of the rotors onto
their respective shafts.
[0025] A preferred embodiment of the present invention provides a
slotted, tapered bushing mated to a tapered hole that comprises the
center hole in a lobed rotor. These two items are placed on a shaft
that has a shoulder against which the rotor rests; a keying
feature, such as a flat, that aligns the bushing; and a threaded
end beyond the keying feature. When the bushing is drawn into the
tapered hole in the rotor by a nut riding on the threaded portion
of the shaft, the rotor is stopped by the shaft shoulder, and the
bushing applies enough force outward to the rotor and inward to the
shaft to fix the assembly rigidly.
[0026] Two such shaft-and-rotor assemblies, counter-rotating,
geared together at a 1:1 ratio, with the two rotors turning in an
elongated cylindrical chamber, comprise a lobed rotor pump. The
number of lobes on each rotor is at least one, and may be any
number for which suitable geometry and manufacturing techniques may
be established. The pump receives feed of fluid or fluidized
material through an inlet at the center of elongation of the
chamber, and sweeps alternating portions of the material around
each half of the perimeter of the combined chamber, expelling the
recombined material through an opening opposite that on the inlet
side. Adjustment of relative rotor angular position to maintain the
dimensional tolerances required for successful use of the pump is
accomplished by unscrewing the locking nut on one of the rotor
shafts, which relaxes the corresponding tapered bushing and
releases the rotor being adjusted. Turning the rotor as required
permits restoration of nominal dimensions; retightening the nut
locks the adjustment in place.
[0027] In FIG. 1, an external view illustrates a preferred
embodiment of the present inventive apparatus and method. A pump
assembly includes a housing 2, an inlet port 4, an outlet port 6, a
set of locking nuts 8 that hold a cover 10 in place, a set of
mounting lugs 12, and a drive shaft 14.
[0028] FIG. 2, which is similar to FIG. 1 but with the locking nuts
and cover 20 removed, shows the inside of a pump chamber 16 of a
preferred embodiment. Two rotors 22 are retained by two nuts 24.
Representative swept pockets 26 within the pump form as the rotor
lobes 28 and 30 on the two rotors move apart from an inlet port 32.
Each pocket 26 moves around the periphery of the chamber, and
collapses as it reaches an outlet port 34.
[0029] An exploded view of a rotor-and-shaft assembly is
illustrated in FIG. 3. Here, a nut 36 may be seen to have an
integral flange 38 and an O-ring groove 40. Flange 38 presses a
tapered bushing 42 into a mating tapered hole 44 in a rotor 46. A
set of slots 48 in the bushing 42 allow the bushing 42 to collapse
without permanent distortion against a shaft 50 when pressed into
tapered hole 44 by the flange 38 on the nut 36. A flat 52 on the
shaft 50 serves as a keying device for the bushing 42. A shoulder
54 on the shaft 50 stops the rotor 46, immobilizing it and allowing
the compression process to proceed. Once the nut 36, bushing 42,
and rotor 46 are fully drawn together on shaft 50, they form a
rigid assembly. Unscrewing the nut 36 allows the bushing 42 to back
out of intimate contact with the rotor 46 and the shaft 50,
permitting readjustment of the rotational orientation of the rotor
46.
[0030] A cross section of a complete pump is shown in FIG. 4. Here,
the first rotor 56 and second rotor 58, oriented as shown in FIG.
2, are seen to occupy all of the volume of a chamber 60 except a
swept pocket 62, which is another view of the bottom swept pocket
26 in FIG. 2. A first drive shaft 64 and a second drive shaft 66
carry their respective rotors 56 and 58. A first spur gear 68 and a
second spur gear 70 mesh to cause rotors 56 and 58 to rotate in
opposite directions. A housing front section 72 and a cover 74
define the chamber. A first nut 76 and a second nut 78 retain first
rotor 56 and second rotor 58, respectively, urging a first tapered
bushing 80 and a second tapered bushing 82 into contact with their
respective rotors 56 and 58, and shafts 64 and 66. The first drive
shaft 64 and first tapered bushing 80 may be seen to be sectioned
through a flat 84 on shaft 64, illustrating the locking
feature.
[0031] The lobe and chamber geometry shown is an example of that
used on large numbers of pumps in manufacturing, although it is not
the only shape capable of pumping with good efficiency. Alternate
lobe geometries may be used.
[0032] Referring to FIG. 3, the number of slots 48 cut in the
tapered bushing 42 is for example eight: four closed at the nut end
of the bushing, three closed at the opposite end, and one cut all
the way through, located opposite the flat. This number is
preferable but other numbers of slots may be used. Likewise, slot
width and web depth may be different from what is illustrated.
[0033] Since pump shaft diameter is defined by torque loading and
safety factors, bushing size is preferably selected within limits
imposed by those factors.
[0034] Bushing taper angle can affect characteristics of the
finished design. Dimensional choices depend on tradeoffs between
several properties of the materials comprising the pump and the
operational characteristics being pursued. Shallower taper
angle--closer to cylindrical--causes tighter clamping with less
applied nut torque, but can lead to binding during disassembly if
excessive. Different surface finishes produce similar tradeoffs.
The taper angle shown, 8 degrees, a surface finish of 32 Ra, and
the material, 316 CRS or other appropriate alloy, have been
determined by engineering experience and test to produce
satisfactory finished products suitable for use in some heavy
production environments.
[0035] With the present invention, each routine disassembly for
inspection and cleaning permits a simple adjustment at need that
restores the rotor-to-rotor clearances to factory specifications
without demounting the pump. By encouraging and facilitating
restoration of original-specification timing during servicing
procedures mandated by regulation, the present invention permits
reduction in the likelihood of pump failure and of production
interruption.
[0036] For the present invention, timing adjustment can be
performed by removal of the materials-handling-side cover,
loosening of the lock nut on one rotor, insertion of spacing shims
between the rotors, tightening, final verification using the shims
at various points as the shafts are rotated, and replacement of the
cover.
[0037] With the present invention, ability to establish timing
accuracy, stability in operation (a function of the rigidity of the
structure), simplicity of inspection, and ability to hold timing
settings over long periods of heavy use can, at the least, remain
as satisfactory as in previous designs. Performance of major
repairs proceeds essentially as before, but routine adjustment
appreciably simplified.
[0038] The many features and advantages of the invention are
apparent from the detailed specification; thus, it is intended by
the appended claims to cover all such features and advantages of
the invention which fall within the true spirit and scope of the
invention. Further, since numerous modifications and variations
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
illustrated and described. Accordingly, all suitable modifications
and equivalents may be resorted to, that fall within the scope of
the invention.
* * * * *